Ultra high frequency device



Feb 18 1947. A. L SAMUEL 2,415,850

ULTRA-HIGH FREQUENCY LINE Filed new. s1. 1942 2 sheets-snee: 1

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ATTORNEY Feb. 18, 1947. A. L. SAMUEL 2,415,850

ULTRA-HIGH FREQUENCY LINE Filed Decfl, 1942 Sheets-Shed 2 vF/G. 4

M/vE/vrbn A. L. SAMUEL A T TOR/VE Y Patented Feb. 18, 1941 UNITED STATESPATENT OFFICE ULTRA HIGH FREQUENCY DEVICE,

Arthur L. Samuel, Summit, N. J., assignor to Bell TelephoneLaboratories, Incorporated, New York, N. Y., a corporation of New YorkApplication December 31, 1942, Serial No. 470,772

7 Claims. l

This invention relates to high frequency circuits and more particularlyto such circuits which employ electron tubes and by-pass condensers inconnection therewith. However, the principle disclosed is applicablegenerally to such circuits requiring a condenser with low impedance athigh frequency.

A principal object of the invention is to provide a high frequencycircuit incorporating a bypass vcondenser in which the by-pass condenserhas an exceptionally low impedance at the operating frequency of thecircuit.

Another object is to provide a cavity resonator type of circuitincorporating conveniently and efflciently a low impedance highfrequency by-pass condenser.

Another object of the invention is to provide for high frequencycurrent, a low impedance bypass between portions of a circuit requiringinsulation between them for direct current.

Another object is to provide a by-pass condenser capable of by-passinghigh frequency current with relatively low voltage between itsterminals.

Anotherobject is to provide such a condenser in a form particularlyadaptable to use with a cavity resonator type circuit.

Another object is to provide a type of by-pass condense;` structuregenerally applicable in producing low impedance high frequencycondensers.

In the use of by-pass condensers in high frequency circuits, difficultyis often encountered due to inadequate by-passing of the high frequencycurrent which results in the impression of unwanted high frequencyvoltage upon the bypassed circuit with attendant undesired radiation andlosses. This occurs particularly at very high frequencies such as wherethe wave-length is of the order of the physical dimensions of theby-pass condenser and under this condition the difficulty may resultfrom resonance effects which set up standing waves throughout thecondenser structure so that regions of high voltage occur at which thecondenser is not effective as a low voltage by-pass.

According to this invention, the difficulty arising from these resonanceeffects is avoided by effectively shortening the lengths of the freetransmission paths in the condenser so that they are less thanone-quarter wave-length at the operating frequency. In this manner, thepaths otherwise long enough to permit resonance are broken up so thatthe standing waves and resulting regions of high voltage or highimpedance are not produced. The transmission paths in a multiplatecondenser are broken up or effectively shortened so far as resonanceeffects are concerned by interconnecting at appropriate points thealternate plates or the interplate spaces. The principle will be moreclearly understood from the following description and the accompanyingillustrations, in which:

Figs 1, 2 and 3 are explanatory to the construction of the by-passcondenser;

Figs. 4, 5 and 6 illustrate the construction of an electronic tubecircuit of which the condenser is a part; and

Fig. 7 is a schematic to make more evident the type of oscillatorcircuit incorporated in Fig. 4.

Where useful, the figures are partially schematic in order to illustratecircuit as well as mechanical characteristics.

Fig. 1 depicts a conventional form of multiplate condenser havingterminals l and 2 and plates 3 to 8 spaced from each other and connectedalternately to the two terminals. When a high frequency voltage isapplied to the terminals, a eld is set up between the plates and currentis transmitted between the terminals. When such a condenser is used as aby-pass to shunt one portion of a circuit to exclude high frequencyenergy from it while completing the high frequency path of anotherportion of the circuit, it is desirable that the high frequencyimpedance of the condenser be low so that considerable current can beby-passed without any substantial voltage being developed across thecondenser and thereby impressed upon the shunted portion of the circuitfrom which it is desired to exclude high frequency energy.

If the frequency is such that the wave-length is comparable to thedistance across the condenser plates, resonance effects prevent auniformly low voltage and effectively increase the impedance of thecondenser thereby decreasing its effectiveness as a by-pass. It may beobserved from Fig. 1 that the condenser plates with the space betweenthem form a transmission line open at both ends and folded as indicatedby the dotted line depicting the longitudinal path. The line conductorsare the plates and the terminal interconnections which together boundthe line in two transverse directions and enclose the electric eld whichis transverse as in one radial direction between the central and outerconductors of a coaxial line. It is evident that if this folded line hassuflicient length, it may resonate when energized so that standing wavesare set up in the electric field and where voltage loops occur, the

voltage between the condenser plates will be relatively high.

A preferred method of preventing this undesirable resonance, accordingto this invention, is shown in Fig. 2 illustrating the modication of acondenser of the type shown in Fig. 1. By this method the longitudinalpath by which resonance occurs is broken up by additionalinterconnections between the plates. -As shown, the free ends ofalternate plates (the ends distant from the terminal interconnections)are additionally interconnected by leads 9 and Ill which pass throughclearance holes in the intervening plates. These interconnecting leadsshort-circuit the folded path loops and thus shorten the free pathlengths over which resonance can occur. For instance, it will be seenthat the longitudinal path partially bounded by the surfaces of plate 1and passing around that plate (first between plates 8 and 1, thenbetween plates 1 and 6) is shunted by the short interconnection of thefree ends of plates 8 and 6 by lead Il) passing through the clearancehole Il in plate 1. If the plates should be appreciably greater thanone-quarter wavelength in extent, additional intermediateinterconnections preferably at random locations will be desirable toadequately break up the longer, otherwise lfree, path lengths. In anycase, interconnections should be provided so that the lengths of freepath are less thanone-quarter wavelength.

Fig, 3 illustrates an alternative method of breaking up the'resonancepaths in the condenser. Here, at locations such as those of theinterconnections in Fig. 2, the interplate spaces are interconnected bythe holes l2, I3, I4 and l5 in the intervening plates. Such holesprovide short paths for the current to pass between opposite surface ofthe plates and as mentioned above in connection with theinterconnections of Fig. 2, additional intermediate holes should beprovided when the plates extend appreciably greater than one-quarterwave-length.

Fig. 4 illustrates an electronictube with a cavity resonator form ofhigh frequency circuit, arranged to function as an oscillator andincorporating a by-pass condenser such as is typified by Fig. 2. This isshown as an example of a practical application of the invention, itbeing understood that the condenser is also applicable to an amplifierarrangement or any other high frequency device requiring a condenserhaving such desirable characteristics. Fig. 5 and 6 show details tofurther illustrate the structure of Fig. 4. Fig. 5 is a section on 5--5of Fig. 4 and Fig. 6 is a perspective view from the top of the by-passcondenser removed from the assembly of Fig. 4. Corresponding parts aresimilarly designated in Figs. 4, 5 and 6. Fig. 1 is a schematicillustrating the type of oscillator circuit incorporated in Fig. 4.

Fig. 4 depicts a continuously pumped vacuum tube which was operated atwave-lengths between 75 and 100 centimeters with plate voltages 3,000 to5,000 and power outputs up to 200 watts. The tube and cavity structuresare generally cylindrical and the iigure shows an axial section, theaxis being vertical. The tube is evacuated through the opening 20, theevacuated space 2l being bounded by the envelope comprising the flatmember 22, the insulating cylindrical glass members 23 and 24, theconducting ilat plate 25, the insulating cylindrical glass members 26and 21 and the cap members 28 and 29. The joints shown where variousmembers come together in the path of the envelope are, of course, madeairtight. The annular plate or anode member 39 with several openingssuch as 3l and 32 to facilitate evacuation and the central oval-shapedopening 33 surrounding the cathode and grid is clamped around the edgesbetween the insulating glass members 23 and 24. The inner surface 39 ofthe opening 33 is the anode surface surrounding the grid structures 34and 35 and the lllamentary cathode members 36 and 31. The gridystructures are connected tothe plate 25 by the metallic grid supportingmember 38. The bypass condenser is made up of the annular plates 43, 44,45, 46, 41 and 48. Plates 43, 45 and 41. are supported by the conductingmember 4l and make contact with member 4l along the outer edges. It willbe seen that the upper nange of member 4I is clamped between members 24and 25 and electrically connected to member 25. The condenser plates 44,46 and 48 are supported by the anode member 30 and make contact withmember 30 around the inner edges of the plates. Plates 43, 45 and 41 areinterconnected electrically near both edges and spaced from each otherbythe pins 50, 5I, 54, 55, 58, 59, 62 and 63 which pass throughclearance holes in plates'44 and 46. Plates 44, 46 and 48 areinterconnected electrically near both edges and spaced from each otherby the interconnecting pins 512, 53, 56, 51, 60, 6l, 64 and 65 whichpass through clearance holes in plates 45 and 41 and the ends of whichare cleared by similar holes in plates 43 as indicated in Figs. 5 and 6.It is evident that the plates are interconnected in the manner shown inFig, 2 with members 4I and 30 in Fig. 4 corresponding to the condenserterminals l and 2 in Fig. 2.

The straight lamentary cathode members 36 and 31 are supported from thecap members 28 and 29 and are insulated from the envelope and other tubeelements by the tubular members 26 and 21. The grid structures 34 and35'surround the cathode members as shown in Fig. 5 and are connectedthrough the supporting member 38 to member 25 and thence to the topflange of 4I.

The cathode members are heated from source 10 through leads 1I and 12which are made the central conductors of coaxial lines with outerconductors 13 and 14. These lines are tuned to one-quarter wave-lengthby the sliders 15 and 16 in the well-known manner to isolate the source10 from the high frequency voltage at the cathode. In the actual device,members 13 and 14 extend along the cathode leads close to member 25 sothat very little of the leads is exposed. The high frequency loadindicated by the resistance is connected between a cathode terminal andthe outer conductors 13, 14 which are connected through the stoppingcondenser 69 to member 25. The grid is biased from source 11 through thepotentiometer and grid leak resistance 18. The plate, or anode, isenergized from source 19 connected to member 30.

The high frequency oscillation circuit has as frequency determiningelements the inductance of the resonant cavity and the capacitancebetween the anode surface 39 andthe grid mem- The resonant cavity isbounded by the members 25, 4l and 30 and the by-pass condenser(comprising plates 43, 44, 45, 46, 41 and 48) Which provides the highfrequency path between members 4I and 30 as Well as insulation for theanode potential from source 19.

The oscillator circuit is of a conventional type as shown in Fig. 7. Theby-pass condenser. de-

scribed above, is designated by the designations of the component platesI3, 44, l5, I6, 41 and 48, the cavity members 25, Il and 30 areindicated and their combined inductance is depicted as the inductiveelement of the circuit and 82 represents the capacitance between theanode surface and grid, the capacitive element of the circuit.

It will be noted that the by-pass condenser is essentially a part of theboundary of the resonant cavity and at the same time is enclosed thereinso as to be completely shielded. This contributes substantially tomaking the oscillation circuit non-radiating.

In the arrangement shown, the by-pass condenser electively coniides thehigh frequency energy and excludes it from the by-passed externalcircuit by virtue of the low high frequency impedance achieved by theinterconnected multiple plate construction despite the large highfrequency oscillation current to be by-passed and despite the fact thatthe condenser plate dimensions are comparable to the wave-length of thatcurrent.

While, for illustration, an oscillator arrangement has been shown,obviously, the principles of the invention may equally well be appliedto other high frequency devices.

What is claimed is:

1. In combination, a space resonator comprising a substantially closedconducting shell having portions insulated from each other for directcurrent and electrical condenser means between the said insulatedportions, the electrical condenser means comprising a plurality ofplates of conducting material arranged substantially parallel and spacedfrom each other, the plates comprising each set of alternate platesbeing electrically connected together and to one of the said insulatedshell portions near one edge of each said alternate plate and beingadditionally electrically connected together near the edges oppositethose connected to a shell portion.

2. A space resonator comprising a substantially closed conducting shelland means for insulating 1 portions of the shell from each other fordirect current, electrical condenser means providing a path for highfrequency current across the said direct current insulating means andbetween the said portions of the shell, the electrical condenser meanscomprising a plurality of plates of conducting material arrangedsubstantially parallel and spaced from each other, the plates comprisingeach set of alternate plates being eleotrically connected to one of thesaid shell'portions by being in contact therewith substantiallycontinuously along one edge of each plate and the plates of each of thesaid sets oi' alternate plates being additionally connected togetherelectrically near the edges opposite those in contact with a shellportion.

3. In combination, a space resonator comprising a substantially closedconducting shell having inner and outer coaxial portions insulated fromeach other for direct current, and electrical condenser means to providea path for high frequency current between the said insulated portions,the electrical condenser means comprising a plurality of electricallyconducting plates arranged substantially parallel, spaced !rom eachother and extending from one insulated shell portion toward the other,one set oi' alternate plates prising the elements of an electricalcondenserl which provides a high frequency' path between the shellportions and therefore a closure for the shell but insulates the shel1portions from each other for direct current, the condenser comprising aplurality of plates of conducting material arranged in substantiallyparallel spaced relation and the plates of each set of alternate platesbeing vconnected together by direct connections at a plurality ofdiscrete points.

5. In a high frequency device, a path for the passage of high frequencycurrent of a given wave-length, the path comprising an electricalcondenser having a plurality of substantially parallel spaced plates ofconducting material the plate surfaces extending distances greater thanone-quarter of the said wave-length and having openings through from onesurface to the other such that high frequency current may be transmitteddirectly therethrough, the openings ybeing spaced such that thedistances over the surface of the plates between direct paths from oneside of a plate to the other is less than one-quarter of the saidwave-length.

6. In a high frequency device, a path for the passage of high frequencycurrent of a given wave-length, the path comprising an electricalcondenser having a plurality of substantially parallel spaced plates ofconducting material, the plate surfaces extending distances greater thanone-quarter of the said wave-length and alternate plates beinginterconnected at points spaced such that the distances over the platesurfaces between at least some of the interconnections are less thanone-quarter of the said wave-length.

7. Means for completing a high frequency electrical circuit by providinga transmission path for high frequency current of a given wavelengthwhile at the same time preventing the transmission of direct currenttherethrough, the said means comprising a plurality oi' substantiallyparallel spaced plates of conducting material having surface dimensionsgreater than one-quarter of said wavelength, alternate plates beinginterconnected at a plurality of points such that the maximum distanceover a plate surface from a point on the surface to an interconnectiondoes not exceed substantially one-eighth of said wavelength.

ARTHUR L. SAMUEL.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,323,201 Carter June 29, 19431,938,857 Pickard Dec. 12, 1933 1,789,263 Nyman (A) Jan. 13, 19311,842,797 Nyman (B) Jan. 26, 1932 2,308,694 Jenner Jan. 19, 19432,171,219 Malter Aug. 29, 1939

